The goals of this application are to gain insight into the molecular, genetic, cytogenetic and cellular processes that affect genetic instability in cells surviving exposure to ionizing radiation. The investigators will first ask whether clinically relevant doses of gamma radiation cause delayed chromosomal instability. They will subsequently investigate whether the instability is a dominant or recessive genetic trait, whether DNA double strand breaks are the molecular lesion that initiate the instability, and try to identify cytogenetic markers of instability.